Antennas are transducers designed to transmit or receive electromagnetic waves. Those used at cellular communications base stations are commonly located on top of buildings, towers or masts to maximise or control the geographic coverage area of the system. The antennas are typically connected with electronic devices such as amplifiers, filters, transceivers etc via one or more coaxial cables. To ease maintenance and historically because of their size, the electronic devices connected to the antennas are conventionally housed remotely from the antennas and are positioned on the ground or in a building. This arrangement has a number of drawbacks which include the high cost of coaxial cables of this type, the RF losses introduced by the cables which can compromise the system performance, possible failure of the cables or the connectors used to attach them to the antennas and equipment, passive inter-modulation distortion due to metal-to-metal contact in the connectors, lease costs associated with the space that the cables occupy, and lease costs associated with the large footprint of the building or of the cabinet housing the electronic device.
As is known, antennas include a feed layer comprising a radiating portion and a feed network. The feed layer in conventional arrangements is located inside the housing or radome of the antenna so as to protect the feed layer from the effects of environmental exposure including rain, wind, sand, UV, ice, etc, and mechanical damage. Such an arrangement is known from the applicant's co-pending U.S. patent application Ser. No. 11/966,501, which describes a cavity-backed, slot-radiating type antenna. In this arrangement, an electrically conducting enclosure has an open or partially open end and a cover. The cover is configured with a slot which is positioned over the resonant cavity formed by the enclosure. The resonance cavity is then excited by or excites the feed layer located in between the enclosure and the cover, such that the higher the volume of the cavity, the greater the bandwidth that can be achieved. This arrangement is however constrained in bandwidth by the need to keep the cavity in the enclosure small, so that the sub-arrays may be arranged in an array at substantially half-wavelength spacing that is required for multi-element array antennas. Furthermore, this slot antenna design requires separate slots for each polarisation.
It would be desirable to provide a broadband antenna with reduced cost and weight that can be connected with (and removed from) an electronic device easily and preferably with the aim of avoiding at least some of the disadvantages associated with connecting an antenna with a remotely located electronic device as described above.